This invention is directed to a flexural mode quartz crystal vibrator and in particular to the placement of electrodes on a quartz crystal plate to improve the utility of a quartz crystal vibrator by reducing the thickness and improving the operation thereof.
Recently, quartz crystal watches have been developed that are practically priced to compete with mechanical watches and the development, manufacture and sales thereof have rapidly accelerated. Such quartz crystal timepieces utilize quartz crystal vibrators to provide a high frequency time standard signal. The quartz crystal vibrators are operated in the flexural mode of vibration, namely, the free-free-bar type or the tuning fork type. Both type flexural mode vibrators utilize a +5.degree. X-cut or a NT-cut quartz crystal plate formed by conventional mechanical process such as diamond wheel cutting, supersonic cutting or the like.
A recent development in manufacturing quartz crystal plates is the chemical processing of a quartz crystal by photoetching the electrodes onto the quartz crystal plate. Such photo-etching has heretofore been only utilized with NT-cut quartz crystal, such flexural mode vibrators formed with a chemically processed NT-cut quartz crystal plate having been disclosed in Japanese Pat. No. 48-3575. X-cut quartz crystal vibrators facilitate the connection thereof into an oscillator circuit due to their low dynamic impedance. Further, they permit precise adjustment of the operating point of an oscillator circuit due to their stabilized flexion-point temperature characteristics at room temperature. However, such mechanically cut quartz crystal plates have heretofore been formed of a thickened crystal plate. The thickness of the crystal plate does not recommend such X-cut quartz crystal plates to an electronic timepiece wherein minimal space requirements are essential. Similarly, although NT-cut flexural quartz crystal vibrators have included small-sized quartz crystal plates which are much thinner than X-cut plates, the dynamic impedance of the NT-cut plates is extremely high and the temperature-resonance frequency characteristic at room temperature is volatile, thereby rendering same less than completely satisfactory.